Aspects of the present invention relate to a nanocomposite (also referred to herein as a “composite”) material for use as an electromagnetic (“EM”) wave or radio frequency (“RF”) (e.g., microwave) absorber or as a filter to trap or remove heavy metals. In aspects of the present invention, a method has been created for a one-pot synthesis (e.g., thermodecomposition process) of magnetic graphene nanocomposites decorated with core-double-shell nanoparticles (“MGNCs”), which can be used for removal of heavy metals, such as chromium. Additional information is included in Jiahua Zhu et al., “One-pot synthesis of Magnetic Graphene Nanocomposites Decorated with Core-Double-shell Nanoparticles for Fast Chromium Removal.” High-resolution transmission electron microscopy and energy filtered elemental mapping reveal a core-double-shell structure of the nanoparticles (e.g., with crystalline iron as the core, iron oxide as an inner shell, and an amorphous Si—S—O compound as an outer shell).
The MGNCs demonstrate an extremely fast heavy metal (e.g., chromium (e.g., Cr(VI))) removal (e.g., from wastewater or water) with a high removal efficiency and with an almost complete removal within at least 5 minutes. The adsorption kinetics follows a pseudo-second-order model, and the novel MGNCs exhibit greatly enhanced heavy metal removal efficiency in solutions with low pH. The large saturation magnetization (e.g., 96.3 emu/g) of the synthesized nanoparticles allows fast separation of the MGNCs from the liquid suspension. By using a permanent magnet, for example, the recycling process of both the MGNC adsorbents and the adsorbed heavy metals may be more energetically and/or economically sustainable. The significantly reduced treatment time required to remove the heavy metals and the applicability in treating the solutions with low pH make such MGNCs promising for the efficient removal of heavy metals from water or wastewater.
Aspects of the invention feature a composition (also referred to herein as a “composite structure” or a “composite material”) that includes a substrate (e.g., graphene), which graphene may be in sheet form or may be in a very small platelet form. This substrate is coated with (or “decorated,” i.e., sparsely covered with) nanoparticles. These nanoparticles may comprise a core of either iron (Fe), nickel (Ni), or cobalt (Co), which is surrounded by at least one shell comprising a material containing silicon and/or sulfur. A thermodecomposition method may be used to produce the metal nanoparticles, which are adhered to the graphene surface. Such a “decorated” graphene substrate may be loaded into a polymeric matrix and formed as needed (e.g., a spray coating, laminate, thin film, honeycomb, foam, etc.). By such a method, a composite structure may be obtained, rather than merely a single piece of graphene powder.
According to aspects of the present invention, such composite materials provide at least two highly useful properties, namely (1) the composite material strongly absorbs RF radiation over a wide frequency range; and/or (2) the composite material efficiently adsorbs heavy metals.
Aspects of the present invention provide a nanocomposite material that may be used in a variety of forms (e.g., bulk material, film, coating, etc.) either as a shield from electromagnetic radiation and/or as an absorber of RF radiation. In aspects of the present invention, methods have been created for making electromagnetic field shielding polyurethane nanocomposites reinforced with core-shell Fe-silica nanoparticles. An aspect of the invention features a composition that includes two-component particles with diameters in a range of nanometers to microns. These components comprise a core made of either iron (Fe), cobalt (Co), or nickel (Ni) surrounded by a shell composed of silica (SiO2) or zirconia (ZrO2) dispersed at high loadings (e.g., greater than 60 wt % of the composite), either randomly or in an aligned fashion. The composition may further include a polymer matrix of polyurethane or any other thermoplastic or thermoset polymeric material.
In a silica coating process that may be used in aspects of the present invention, iron particles (e.g., carbonyl iron particles “CIP,” e.g., 3.0 g) may be dispersed in a solvent (e.g., 120 mL ethanol) containing 3-aminopropyltriethoxysilane (“APTES,” e.g., 0.4 mL at room temperature). After mixing (e.g., 30 minutes of sonication), the obtained suspension may be allowed to age (e.g., for 1 hour) to arrive at a complete complexation reaction between the amine groups of APTES and the CIP surface. Gelatin B (e.g., 1 wt %, 20 mL solution) may be also used to functionalize the CIP surface, which may have a primer effect on the final shell morphology. The CIP may be coated with a layer of silica (e.g., by a modified Stöber process). The suspension may be vigorously mechanically stirred (e.g., 500 rpm). Different amounts of tetraethyl orthosilicate (“TEOS,” e.g., 1.8-5 mL) and ammonia (e.g., 12-16 mL) may be used in the reaction system to control the silica shell thickness. TEOS may be injected into the suspension and followed by an addition of ammonia (e.g., dropwise for about 5 minutes (“min”)). The reaction may be continued (e.g., for 5 hours) and then the powders separated from the mother liquid (e.g., using a magnet). The powders may be washed (e.g., with ethanol and DI water several times) and then dried (e.g., in a vacuum oven overnight at room temperature) to obtain core-shell CIP-silica particles (also referred to herein as “CIP-silica”). A final annealing of the CIP-silica may be performed (e.g., at 650° C. for 2 hours under H2/Ar atmosphere (hydrogen ratio: 5%)), with an aim to complete the reaction from TEOS to silica and reduce the iron oxides.
Polymer nanocomposites in accordance with aspects of the present invention may be synthesized as follows. The CIP (e.g., 7.0 g) may be initially mixed with a diluted mixture solution containing an accelerator part A (e.g., 0.36 g), a catalyst part C (e.g., 0.40 g), and THF (e.g., 20.0 mL), followed by mixing (e.g., 1 hour sonication at room temperature) to allow the adsorption of the accelerator part A and the catalyst part C on the CIP surface. Then a monomer part B (e.g., 2.24 g) may be added to the suspension and mechanically stirred together (e.g., at 200 rpm in an ultrasonic bath for one hour at 50° C.). The suspension becomes more viscous as the reaction proceeded. The viscous suspension may be transferred into a mold (e.g., and maintained at room temperature for an additional 7 days) to further the reaction and solvent evaporation. Composites with the same loading of CIP-silica (e.g., shell thickness: 55 nm) may be fabricated following similar procedures. A CIP-silica/PU composite thin film (e.g., thickness: ˜10 μm) on glass slide may be prepared from the THF-diluted composite solution (e.g., by using a drop casting method).
The composite may then be fabricated into a variety of forms as dictated by the application (e.g., a composite part, a coating, a skin or laminate, or any other form into which polymeric materials can be formed). The shape can be easily controlled because the processing starts from a liquid and because the curing does not require any special heat treatment. Such materials exhibit high RF absorption over a wide range of frequencies (MHz to GHz regions), which properties can be controlled by virtue of the properties of the nanoparticle fillers. For example, the specific microwave absorption properties may be tailored by varying the size and/or composition of the particles, and/or the composition and thickness of the matrix.
With respect to RF adsorption, currently available materials for RF absorption typically either exhibit high RF adsorption over a narrow frequency range, or they exhibit relatively low absorption over a broad frequency range. In contrast, the composite material in accordance with aspects of the present invention is an easily moldable and processable material, which exhibits high RF absorption over a broad frequency range. Some aspects of the present invention exhibit high RF absorption over a broad frequency range between about 10 Hz and about 106 Hz. Some aspects of the present invention exhibit high RF absorption over a broad frequency range between about 1 Hz to about 20 GHz. At a high RF absorption, radiation will be prevented or significantly reduced to generally acceptable levels.
Commercial applications utilizing this RF absorption property include shielding for electronics, low observable materials (e.g., reduction of detectability via radar) for defense applications (e.g., airplanes, missiles, and ships), and electronic components. For example, refer to FIG. 33 showing electromagnetic shielding from an EM source 3301 in which the composites of the present invention are molded into a polymeric matrix to form the packaging 3302 for inhibiting the EM waves from escaping from the product 3300, such as a cell phone. Aspects of the present invention are generally much lighter materials that can enhance microwave absorption performance with an intensified absorption and a broad absorption wave gap.
Additional information on the foregoing is included in Jiahua Zhu et al., “Electromagnetic Field Shielding Polyurethane Nanocomposites Reinforced with Core-Shell Fe Silica Nanoparticles,” J. Phys. Chem. C, 2011, 115, 11304-15310 (published Jul. 5, 2011), and Jiahua Zhu et al., “Silica Stabilized Iron Particles toward Anti-corrosion Magnetic Polyurethane Nanocomposites,” (2011).
Background information is included in Chun-Ling Zhu et al., “Fe3O4/TiO2 Core/Shell Nanotubes: Synthesis and Magnetic and Electromagnetic Wave Absorption Characteristics,” J. Phys. Chem. C, 2010, 114, 16229-16235 (published online Sep. 9, 2010).
With respect to chemical filtering (or trapping) of heavy metals, currently, activated carbon is the material most commonly used for filtering of heavy metals. Aspects of the present invention adsorb a greater quantity and/or percentage of such much more heavy metals than such activated carbon. Furthermore, aspects of the present invention implemented in a polymeric matrix are also more easily formable and more durable than activated carbon. Commercial applications utilizing the absorbance property include filtering of fluids (e.g., water) containing heavy metals for environmental remediation or for industrial processes.
In aspects of the present invention, carbonyl iron particles (“CIP”) may be coated with silica by using both gelatin and 3-aminopropyltriethoxysilane (“APTES”) as primers to promote the deposition and adhesion of silica on the CAP surface. The silica shell thickness may be controlled through adjusting the concentrations of tetraethyl orthosilicate (“TEOS”) and ammonia. Polyurethane nanocomposites filled with either bare magnetic CIP or silica-coated CIP may be fabricated with a surface-initialized polymerization (“SIP”) method.
The examples provided herein are to more fully illustrate some of the aspects of the present invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute exemplary modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific aspects that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
All patents and publications referenced herein are hereby incorporated by reference herein. It will be understood that certain of the herein described structures, functions, and operations of the aspects are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or aspects. In addition, it will be understood that specific structures, functions, and operations set forth in the referenced patents and publications can be practiced in conjunction with the aspects of the present invention, but they are not essential to its practice. It is therefore to be understood that aspects disclosed herein may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention as defined by the appended claims. Furthermore, specific parameters are provided herein, such as quantities, temperatures, etc., but it should be understood that aspects of the invention are not limited to these exact parameter values, but may be approximate and still enable such aspects of the invention.